Electrical condenser



Oct. 20, 1.942. F. w. GQDSEY, JR 2,299,271'

ELECTRICAL comrsnsnl Filed July 3, 1 940 y 77` seals/5:55a ci@ 79 7af aeg.;

a2 l f f' 6 r v. H A @a L l A'- 5 a5 aa FRANK #f 6005?, JR. INVENTOR.

ATTORNEYi Patented Oct. 20, 1.942

ELECTRICAL CONDENSER Frank w. Godsey, Jr.. North Adams, Masts., as-

signor to Sprague Specialties Co., North Adams, Mass., a corporation ot Massachusetts Applicatln Jllly 3, 1940, Serial No. 343,871

6 Claims.

The present invention relates to electrical condensers and more particularly to ilxed and adjustable condensers particularly adapted for use `as padder" and tuning condensers in radio receivers.

To be suitable for such use, condensers must meet several important requirements. For example, they must combine a high capacity value with a small volume, must be of rugged construction to withstand Wear and vibrations, and be adapted for low cost, mass production. Furthermore, they must be stable, i. e. maintain their adjusted capacity setting even if the condenser is subjected to a wide-range heat cycle.

It is therefore an object of my invention to provide an adjustable condenser which meets all of the above requirements, and which is very small for a given capacity value, is of rugged construction, inexpensive to produce, and exhibits a very high degree of electrical and mechanical stability.

To counteract the changes of the electrical constants of the components of the tuned circuits and particularly the changes in the constants oi the tuning coil of such circuits brought about by the wide-range temperature variations encountered in the operation of a radio receiver, and the ensuing changes in the resonant yfrequency oi such circuits, so-called compensating condensers are used in these tuned circuits whereby as a rule one compensating condenser is needed for eachl tuned circuit.

Such use of individual compensating condensers for each tuned circuit has several disadvantages, chief among which are the high cost and increased complexity of assembly. Because of this, there have been endeavors to provide condensers which do not require separate compensating condensers but serve simultaneously both as tuning condensers and as compensating condensers. Such prior attempts, however, have been unsuc cessiul because of the erratic and unpredictable compensating characteristics of such prior condensers. y'

It is therefore a further object of my invention to provide a novel condenser capable of serving both as a tuning and as a compensating condenser of a tuned circuit, and which obviates the diiculties of prior condensers of this type.

These and 'further objects of my invention will appear as the specification progresses.

'I'he invention will be described with reference to the appended drawing forming part oi the specification and in which:

Figure 1 is a partly sectionized side View of an adjustable condenser made in accordance `with the invention.

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1, also showing the mounting means of the condenser, which are not shown in Fig. 1.

Fig. 3 is a side view of a second embodiment oi! the invention.

Fig. 4 is an end view of the condenser of Fig. 3.

Fig. 5 is a side view of a dual unit condenser made in accordance Withthe invention.

Fig. 6 is a side view of a. condenser in accordance with the invention for the simultaneous tuning and compensating of a tuned circuit.

Fig. 7 illustrates another embodiment of a combined tuning and compensating condenser made in accordance with the invention.

Referring to Figs. l and 2, the condenser there shown comprises two concentrically disposed electrodes I0 and II. Electrode I0 consists oi a metal cylinder or preferably a hollow sleeve closed at one end, whereas electrode I I consists of the effective portions of a wrap-around metal clamp encircling the electrode I0 and to be more vfully described later. Interposed between electrodes I0 and I I is a concentric dielectric layer I2 forming an integral coating on the surface of electrode I0. The dielectric layer I2 consists preferably of a potassium lead silicate vitreous enamel, as disclosed in the copending application of Stanley O. Dorst, Ser. No. 289,292 filed August 9, 1939, noW U. S. Patent No. 2,290,947 issued July 28, 1942, which is cataphoretically applied to the electrode I0. TheY layer i2 may also consist of other suitable dielectric materials, for example, of various kinds of vitreous enamels, or may consist of a non-vitreous dielectric material such as of cellulose acetate, polystyrene, hard rubber or the like, to which dielectric materials may be added a filler of titanium dioxide or other dielectric material to increase the dielectric constant and/or lower the power factor.

The layer I2 is applied to the electrode l0 preferably by the cataphoretic deposition process described in the copending application of Preston Robinson et al., Ser. No. 197,692 filed March 23, 1938, which produces a coating of high uniformity and of even thickness throughout tne length oi. the coating. As a rule I prefer to also fuse the so-deposited coating and to subject it thereafter to surface grinding as described in the copending application of Robert C. Sprague and Frank W. Godsey, Jr., Ser. No. 336,822, iiled May 23, 1940.

The offset wrap-around metal clamp, comprises a ilat rectangular strip portion I3, which extends into two integral and substantially annular segmented outer sleeve portions. I4-I4,'and a simiresponding hole of the' ap 58 and threadedly engages a threaded bore of iiap 55.

lar but wider middle. portion I5. The portions I4-I4 and I5 surround the coated electrode I8 and form the complementary electrode thereto.

The sleeves I4-I4 and I5 extend into rectangular naps I8-I8 and I1 respectively, bent parallel with and disposed adjacent to the strip I3. The ilaps I5-I5 are each iixedly secured to the strip I3 by rivets I8-I8 or similar fastening means, to press the sleeves I4I4 with a high and constant pressure against the dielectric layer I2 underlying same.

The capacity of the `condenser is adjusted by` tightening or loosening the bolt 59 whichcor- The ap I1 is adjustably secured to the strip z,

I8 by means of a bolt lswhichpasses through a corresponding hole of the strip I8 and threadingly engages the ap I1.

The condenser is mounted on va base, for example, as shown in Fig. 2, on the metal chassis 22 of the radio receiver, by means of rivets or bolts 23--23 engaging holes 2I2I of strip I3.

The capacity of the condenser is adjusted by means of the bolt I8 which depending on its adjustment causes `the segment I5 to exert. a'

greater or lesser pressure on the dielectric layer I2, resulting in the lformation of an air-gap of smaller or larger thickness between the segment res ndinglyincreases or decreases the pressure exerted by sleeve 54 on the dielectric layer 5I,

`and in the range of the minimum capacity settings causes a tapered'air gap 80 to form between the electrode 52 and the dielectric layer 5I.

The condenser is mounted on a suitable base, for example, a metal chassis 55, by means of a bracket 5,1 which as shown may consist of an extension oi' the ap 53 and is provided with two right angle ben`ds. The bracket 51 is secured to the base 55 by means of a rivet 83.

Outside electrical connection to electrode 50 `is established through the metal chassis 58 and I5 and the layer I2. For the convenient adjust- Y ment of the bolt from either side of the condenser, both the head and the endlof the bolt are preferably slotted, and the chassis 22 is cut out at 21, to permit passage of and access to the head of bolt I9.

Outside electrical connection to the electrode II is provided as a rule by the metal chassis itself. If a nonconducting mounting base is used, a. terminal lug 24 is provided which can be secured to the strip 'I3 by the rivet 23. Electrical connection to the electrode I8 is provided by a terminal lug 25, securedto the uncoated end-y face of the electrode I0, for example, by means of a rivet 26.

The condenser shown inFigs. 3 and 4 comprises van inner cylindrical electrode 5B consisting of a preferably hollow, metal cylinder or sleeve and a dielectric layer 5I preferably of a vitreous dielectric material applied to the electrode 50 as an integral coating thereon. The electrode 50 and the dielectric layer 5I conform to the requirements stated for the corresponding elements I0 and I2 of the condenser of Figs. l and 2.

The outer and adjustable electrode of the condenser consists of an unidivided substantially cylindrical or sleeve portion 54 of a wrap-around metal clamp 52 and surrounds the electrode 55. The sleeve 54 extends into a longer iiap 53 and a shorter flap 55, the two being bent radially in parallelism along the lengthof the shorter ap.

Whereas to facilitate the mounting of the condenser of Figs. 1 and 2, the wrap-around clamp to the inner electrode 54 through a terminal lug 8| which is secured to its end-face by means oi' a rivet 52.

In Fig. 5 the invention i's shown as applied to a dual unit assembly consisting of a ilxed condenser 10 and ofan adjustable condenser 1I.

Thev condensers 10 and 1I have a 'common inner electrode which consistsof a hollow metal cylinderor sleeve 12 closed at one endvand provided o n its surface with an integral coating or layer 13 of a .vitreous dielectric material such as described in connection with the condensers of Figs. 1 to 4.

The xed capacity condenser 10 comprises a i wrap-around metal clamp 14, having a cylindrimember II is formed with an offset portion,V

whereby the iiaps extend tangentially to the sleeve electrodes, in practice as a rule I prefer to use the construction shown in Figs. 3 and 4, in which the flaps of the sleeve extend radially, and the sleeve electrode is in direct contact with the dielectric layer throughout its major area.

The flaps 53 and 55 are pivoted and held together at one end of their opposing faces byv means of a rivet 58, whereas at the other end they are adjustably clamped together by means of a bolt 59. The bolt 59 passes through a corcal or sleeve portion 11 forming the outer electrode which surrounds the electrode 12 and is in contact with the dielectric layer 13. The sleeve 11 extends into flaps 15 and 16 which are held together by the rivet 18 which also secures' a terminal lug 18 serving as outside electrical connection forelectrode 14.

The adjustable condenser 1I comprises a wraparound metal clamp Bn having a nat strip portion 8l, two cylindrical sleeves 82 and 83 forming the outer electrodes and being independent of each.

other but integral with strip 8i. The sleeves l82 and 83 surround the inner electrode 12 and extend into iiaps 84 and 85 respectively. The sleeve 33 is pressed, with constant high pressure, into intimate contact with the dielectric 13 by means of a rivet 86 which passes through and clamps together the flap and the \strip 8l, thereby The closed end of electrode 10 is provided with an axial tapped bore for receiving a suitable mounting bolt, by means of which the condenser assembly can be mounted on a suitable prefera-k bly metal base which in practice also serves for electrical connection to the electrode.

Willie the invention has been described so far, in connection with condensers having a single function, for example, serving as padder or tuning condensers, the novel construction ofthe invention is particularly adapted for imparting to such condensers compensating characteristics. This I achieve, by making the inner and the outer electrodes of the condenser ot different metals of such characteristics. that with increasing temperatures the outer electrode expands radially to a greater or lesser extent than does the inner electrode. Such differential expansion of the two electrodes,'causes the outer electrode to exert a greater or a lesser pressure on the dielectric layer orto form a lesser or greater air gap between these two elements thereby correspondingly varying the capacity of the condenser. As a rule, increasing temperatures so change the constants of the tuned circuits of radio receivers as to cause the resonant frequency of the circuit to decrease, in which case I impart Vto the condenser a negative temperature coefllcient of capacity by making the outer sleeve electrode of a metal having a greater temperature coefllcient of linear expansion than has the metal of the inner electrode. For example, I make the outer clamp-around electrode of brass and the inner electrode of iron.

A condenser capable of performing simultaneously as tuning condenser and compensating condenser is shown in Fig. 6. The condenser as shown, comprises an inner electrode consisting cfa hollow metal cylinder, and a dielectric layer |0| of a vitreous dielectric material which forms an integral coating on the electrode |00. The outer electrode of the condenser consists of sleeve portions of a wrap-around metal clamp which, in this instance, are made up of two separate 4but mechanically and electrically interconnected members |02 and |03. Members |02 and |03 comprise spaced annular portions ||5 and ||0 respectively, which form the outer electrodes and surround the electrode |00. The portions ||5 and ||6 are provided at their two ends with flaps |00-|03 and |05|06 respectively. The member |03 isfixedly held about the coated electrode |00 and in contact with the dielectric layer |0| by means of a rivet |04 passing through and securing together the iiaps |05 and |06. The member |02 is secured about the coated electrode |00 by means of an adjustable bolt |01 passing through the flap |08 and threadingly engaging the flap |09.

The members |02 and |03 are interconnected bya metal strap ||2 secured by rivets ||0 and passing through the iiaps |06 and |08 respectively. y

A terminal lug |20 secured to the flap |00 by rivet serves for the outside electrical connection of the outer electrodes, whereas for such connection of electrode |00 there is provided a lug |2| secured to its end-face, by a. rivet |22.

To impart to the condenser the dual function of tuning and compensating condenser, one or both of the members |02 and |03 are made of a metal having a different temperature coefiicient of linear expansion than the metal of electrode |00. Such embodiment of the invention lends itself to various combinations of compensating condensers.

For example, by making the xedly positioned member |03 of brass, and the electrode |00 and the adjustable member |02, of iron and steel respectively, I obtain an adjustable tuning condenser having a substantially constant negative temperature coefficient of capacity. Or by making the adjustable member |02 of brass, and the electrode |00 and the member |03 of iron and steel respectively, a combined tuning and compensation condenser is obtained which has a negative coeicient of capacity, changing proportionally to the vcapacity setting of the condenser.

In Fig. 'I is shown another embodiment of a 7 combined tuning and compensating condenser. The condenser there shown comprises an inner electrode |30 consisting of a hollow metalicylinder, and a dielectric layer |3| consisting of a vitreous dielectric material and forming an integral coating on the surface of electrode |30. The outer electrode consists of a sleeve portion |33 of a wrap-around metal clamp member |32 which extends into two contacting iiaps |34 and |35. The flap |34 extends Ibeyond flap |35 into a mounting bracket |36 by means of which the condenser is secured by ay rivet |39 to a suitable, preferably metal base |40. The flaps |34 and |35 are adjustably secured together by means of a bolt |31 whichk passes through the `iap |34 and threadedly engages the ,ilap |35. interposed between the head of bolt -|31 and the flap |34, is a spacing sleeve |38. External electrical connection to electrode |30 is provided by a terminal lug |4| secured to the end of electrode by a rivet |42 whereas connection to the outer electrode is provided through the metal chassis |40.

The compensating action of the condenser is here produced by making the bolt |31 and the spacing sleeve |30 of materials having different coefficients yof linear expansion. By so doing, temperature variations cause a differential expansion of these elementsresulting in a change in the pressure exerted by the wrap-around member |32 on the dielectric layer |3|, causing the air gap between these two elements to correspondingly vary.

To produce a condenser with a negative temperature coeiiicient of capacity, the bolt |31 is made of a material with a. greater temperature` ,coeiiicient of expansion than the spacing sleeve |30, whereby with increasing temperature, the

greater linear expansion of the bolt |31 causes a decrease in the pressure exerted by electrode |32 on the dielectric |3|. This can be achieved, for example, by using a. sleeve |38 of Isolantite and a bolt |31 of brass. The degree of compensation produced in the condenser is determined by the difference in the respective temperaturev coefiicients of the materials of the bolt |31 andthe vsleeve |38 and the geometrical relationship of these members.

While I have described my invention with reference to specific examples and in specific embodiments, I do not Wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

1. An electrical condenser comprising-a cylindrical electrode and a dielectric layer forming an integral coating on the surface of said electrode, a wrap-around metal clamp comprising a plurality of interconnected segments forming coaxial electrodes around said coated electrode, one of said segments being fixedly secured about said inner electrode, and another of said segments being adjustably secured about said inner electrode.

2. An adjustable electrical condenser comprising a cylindrical electrode and a dielectric layer forming an integral coating on said electrode, a wrap-around metal clamp comprising a sleeve member serving as a second electrode, said sleeve member coaxially surrounding the coated electrode and contacting said dielectric layer, a first portion of said sleeve fixedly secured in pressure contact with said dielectric layer, and means to adjust the capacity of the condenser comprising amember adapted to vary the consleeve portion, said sleeve portion constitutingl the second electrode of the condenser and surrounding said coated electrode. said naps contacting eachother with their inner faces and being iixedly secured to each other at one end of their faces and maintaining the corresponding portion of the sleeve in ilxed pressure contact with the dielectric layer, said flaps being adjustably secured to each other at the other end of their faces. n

4. An electrical condenser assembly comprising a plurality of condenser units comprising a common cylindrical electrode and a dielectric layer forming an integral coating on the surface of said electrodel and individual wrap-around metal clamps each comprising a sleeve member and constituting the second electrodes for each condenser, said sleeve members coaxially surrounding the coated electrode and contacting said dielectric layer, one of said sleeve members comprising a rst portion maintained in a xed pressure contact with said dielectric layer and a second portion in adjustable pressure relationship with said dielectric layer.

5. An adjustable condenser comprising a cylin- `drical electrodeand a. dielectric layer forming an integral coating on the surface of said electrode, a plurality of wrap-around metalclamps each `comprising a sleeve member constituting the second electrode of the condenser, said sleeve members ccamally surrounding the coated electrode and contacting said dielectric layer, one of said sleeve members xedly maintained in pressure contact with said dielectric layer anda second sleeve member in adJustable pressure relationship with said dielectric layer, a member rigidly securing together said first and second sleeve members, one of said sleeve members consisting of a metal having a different temperature coeillcient of linear expansion than the inner electrode. v 6. An electrical condenser comprising a cylindrical electrode and a dielectric layer provided on said electrode, a wraparound metal clamp comprising a sleevemember constituting the second electrode, said sleeve surrounding the coated electrode and contacting said dielectric layer,

said sleeve comprising a plurality of interconnectd segments provided with extending aps,

means fixedly securing together a rst set of ilaps, 

